Alkaloids color tests

Thalictine (60), C37H40N2O6, an amorphous, air-sensitive base, was isolated from Thalictrum thunbergii D.C. as its nitrate salt, mp 226-228°C. The alkaloid shows [a]D -15.8° (CHC13), -12.2° (MeOH), IR 3550 cm"1 (OH), and it gave a positive ammonium phosphomolybdate color test for a cryptophenol. The... 

Mecambroline was isolated from Meconopsis carnbrica Vig. (Papaver-aceae), and the elemental data indicated the value C18H17O3N. The alkaloid melts at 145°, and exhibits [aj +76° (in CHCI3). A hydrochloride salt was obtained (inp 264°-266°) as well as a picrate (mp 179°-180°). Color tests showed the presence of a methylenedioxy and a phenolic group. The UV-spectrum had 308 and 275 mp, (log e 4.0 and 4.2), with a shoulder at 269 mp (log e 4.1), typical of a 1,2,10-tri-substituted aporphine. 0-Methylation with diazomethane gave a base (mp 111°-112°) 6). 

Newer methods of chemical analysis led to the isolation of the major alkaloids from crude drug preparations. By 1833, aconitine, atropine, codeine, hyoscyamine, morphine, nicotine, and strychnine had been isolated from plants. Color tests for alkaloids were developed between 1861 and 1882 by 1890 quantitative analysis methods became available. Physiological tests for alkaloids, particularly strychnine, first used in 1856, were employed well into the twentieth century. Tests for alcohol, devised by Lieben (iodoform crystal test, 1870) and others, were later perfected for the quantitative analysis of alcohol in body fluids and tissues. Qualitative tests for carbon monoxide in the blood were developed about this time and in 1880, Fodor developed a palladium chloride reduction method to quantitate carbon monoxide in blood. 

The evaluation of alkaloids content may be effected on the basis of color tests by the Van Urk reaction (Pharm. Weekbled 66, 1929, p. 473) after extraction as follows the culture broth is alkalinized to pH 8 and extracted first with chloroform and then re-extracted with the aqueous acidic solution (e.g., 1% H2S04 or 2% tartaric acid) which is used for the colorimetric analysis of alkaloids. 

Until about 20 years ago the only way in which an alkaloid isolated from cadaveric material could be identified was by means of color and crystal tests. Both of these date back for well over a century, the color test being the older of the two. It has the great advantage of speed and simplicity and is ideally suited to rapid screening procedures. It has recently secured a new lease on life owing to the way in which it may be used for locating compounds on paper and thin-layer chromatograms. 

Few color tests are specific, but many have the advantage that they will work satisfactorily in the presence of a high proportion of impurity. Color tests for many alkaloids have been described (331-334). 

THE FORENSIC CHEMISTRY OF ALKALOIDS TABLE V Color Tests ... 

A color test utilizing isatin for piperidine and pyrrolidine alkaloids containing the structural unit — NH—CH2—CH2— has been described (53). Coniine and conhydrine give a positive test but pseudoconhydrine, which lacks the above feature, does not. The Conium alkaloids have been separated by gas-liquid chromatography (54). 

In the development of disease resistant varieties, secondary alkaloids are often a concern for flue-cured tobacco breeders. A rapid color test developed by Glock and Wright (1963) is used to quantify nornicotine in flue-cured tobacco. The method involves color development from the reaction of nornicotine and 1,3-indanedione. This test is sensitive enough to detect microgram levels of nornicotine. The method is used quantitatively with a spectrophotometer because color development is linear from 5.0 to lOOpg/ml of nornicotine reacted with 1,3-indanedione. 

Cobalt thiocyanate A reagent used for a color test for cocaine and related tropane alkaloids. 

Marquis Reagent A color test reagent that reacts with a variety of controlled substances, principally alkaloids. 

A wide range of color tests of -arying degrees of aensithity and specificily ha e been reported for the detection of formaldehyde in addition to the two authenticated methods already described. These tests involve the use of phenols, aromatic amine. , alkaloids, and other miscellaneous reagents. 

This section includes representative examples of the major types of reactions that are encountered in bisbenzylisoquinoline alkaloid research. Some of this material is not otherwise covered in this work. Diagnostic procedures, such as solubility tests and color reactions, are not considered. 

This reagent is prepared by dissolving 1 g of /7-dimethylaminobenzaldehyde in 10 ml of methanol and adding 10 ml of concentrated phosphoric acid. The reagent is then added directly to the test substrate. A grey/violet coloration is produced with those compounds containing the indole alkaloid nucleus (e.g. LSD and psilocin). 

In many cases, however, the saprophytic cultures of ergot described in the literature were tested for the presence of ergot alkaloids not only by means of color reactions, but also by biological methods (e.g. uterotonic activity). Nevertheless, when applied to complex material such as culture filtrates or extracts of mycelium, these methods of examination cannot be regarded as specific either, since other substances, e.g. histamine, also exert a more or less marked uterotonic action. 

---